Whether it's Japanese Slow Jogging or Niko Niko (little difference), or shuffling (see the videos below) ... this is the way* to approach C25K as a 1st timer.
Nice and easy - there should NO struggle, no pain , no breathlessness (a sure-fire clue) and you should be able to EASILY hold a conversation - call it a 'chatty pace' if you like.
*although I don't agree with the whole heel-striking thing
youtube.com/watch?v=9L2b2kh...
youtube.com/watch?v=ep3vRgO...